High power gas and solid state lasers have gained acceptance in manufacturing today by reducing costs and improving product quality. The utilization of such lasers as a percentage of the time they are available for use is, however, low. This is the case since, typically, such applications are set up on a one laser per workstation basis. As a result, these applications experience a high set-up to process time ratio and a large capital cost per workstation.
A design objective of such laser workstations is to provide flexibility in applying the beam generated by a single laser, e.g. to effect a weld, at a plurality of physically different locations. Such flexibility serves to improve laser utilization. One technique known in the art for providing such flexibility is to direct the laser beam through one end of an optical fiber so that the other end of the fiber may be moved between a plurality of different locations on a workpiece. Apparatus for the practice of such a technique is disclosed in U.S. Pat. No. 4,564,736. A second technique known in the art for providing such flexibility is to divert a laser beam among different points on a workpiece and/or between workstations by means of mirrors and refracting elements. Typically, the total distance that the beam of a commercially available rod laser can travel, before diverging to an unusable size, is small (e.g. less than 2 meters). Thus, the total number of work stations among which a laser beam can be diverted is greatly limited by the total distance the beam can travel. As a result, improvement in laser utilization that can be achieved by diverting the laser beam in this fashion is limited. A third technique known in the art to increase flexibility of laser use is to split the laser beam into multiple portions each of which is diverted to a different work location. A substantial drawback to this technique is the reduced laser power, caused by the beam splitting, delivered to each work location.
Uses of lasers in marking applications are known in the art and comprise apparatus for directing a laser beam onto a surface for the purpose of scribing information thereon. One type of apparatus for marking (writing) with a laser beam utilizes a pair of galvanometer driven mirrors which respectively deflect, or scan, the beam alng "x" and "y" orthogonal directions. The galvanometer movements are controlled to cause the desired information to be written. Such applications include a focusing lens to focus the laser beam to a small point to provide readable characters. Usually such marking applications employ post-objective scanning wherein the beam is passed through the focusing (objective) lens before being diverted or scanned by the mirrors. One desirable feature of post-objective scanning is that the diameter of the beam is small when it strikes the mirrors, thereby enabling the use of small mirrors. The small mirrors have a relatively low inertia so that faster galvanometer movement and increased operating speed of the marking apparatus are possible.
There are marking applications in which pre-objective scanning is employed. The difficulties in applying pre-objective scanning in marking applications are described in the paper entitled "Precision, Post-Objective, Two-axis, Galvanometer Scanning" by Kurt Pelsue, Society of Photo-Optical Instrumentation Engineers, Volume 390, 1983, which is incorporated in its entirety herein by reference. Due to the high accuracy required in beam placement and the fact that a relatively large diameter unfocused beam is scanned by the mirrors over the focusing lens, a special f-.theta. lens is required. As described in the above cited paper, the f-.theta. lens is used to implement corrections into the laser beam incident thereon. However, the f-.theta. lens introduces distortions into the scanned pattern on the marked surface. Further, the design of the f-.theta. lens is unique to the parameters of the system in which it is implemented so that minor changes in system of configuration necessitate expensive lens redesign and fabrication. Thus, for these reasons also, post-objective scanning is preferred in marking applications. A different type of marking application utilizes one or more nonlinear optical crystals, instead of the mirror and galvanometer combination described above, to scan the laser beam over the marked surface. Such optical crystals change their refractive index in direct proportion to an applied voltage. Characteristic of optical crystal applications and a major drawback thereof is that very high voltages (on the order of kilovolts) are required to produce minute beam deflections. This necessitates providing the components to generate and modulate the high voltages. Further, the beam deflections so produced are small, thereby limiting the utility of the crystals in such applications.
It is an object of the present invention to provide apparatus which enables substantial improvement in power laser utilization and reduction in capital cost per workstation.